function* gen() {
//   try {
//     let result = yield "2 + 2 = ?"; // (1)

//     console.info(
//       "The execution does not reach here, because the exception is thrown above"
//     );
//   } catch (e) {
//     console.info(e); // 显示这个 error
//   }
// }

// let generator3 = gen();

// let question3 = generator3.next().value;

// generator3.throw(new Error("The answer is not found in my database")); // (2)